Replacing some of the cocoa butter with milk fat can control fat bloom in chocolate, according to new research from Canada.

Fat bloom frequently results in significant product losses for confectionary manufacturers as, although it does not affect the taste, the tell-tale sign of the bloom - a white frosting - is unacceptable to consumers.

Fat bloom is a consequence of changes in the fat structure of the substance and can be caused by inadequate cooling processes whereby tiny temperature fluctuations as small as plus or minus 2°C can cause cocoa butter crystals to melt and then recrystallise, forming large cone-like structures that scatter light giving a dull appearance.

Food science professor at Ryerson University, Derick Rousseau, was the lead researcher in a study published in Food Chemistry that found that the partial replacement of cocoa butter (five per cent) with milk fat (MF) in chocolate manufacturing reduces the incidence of large surface crystals and the number and diameter of cones.

The results also show that the addition of MF decreases the surface roughness and the rate of surface coarsening.

The amount of milk fat is crucial, claims Rousseau, with the study demonstrating that the addition of 7.5 per cent MF made for a chocolate too soft to handle with a lack of snap and poor melting properties.

“The addition of five per cent MF was a suitable compromise between maintaining the sensory properties of chocolate and robustness to temperature cycling,” he continued.

He said that the results show that milk fat reduces the initial solid fat content, and slows the rate of change in whiteness index.

Rousseau also found that the fat crystal growth is accelerated by repeated temperature-cycling compared to isothermal conditioning but that cone hardening occurs more rapidly when isothermally-stored.

Irrespective of fat composition and storage conditions, fat crystal growth, welling and ultimately fat bloom begin only at specific locations on the chocolate surface, he added.

He said that this suggests that chocolate’s microstructural heterogeneity is responsible for distinct surface fat crystallisation pathways.